Many mechanical and metrological applications involving linear and rotary movement of parts or articles transported by mechanical means require supervision. The supervision frequently requires knowledge about the absolute position of these parts or articles. To address this need, many types of absolute position encoders have been developed. In general, they include linear position encoders and rotary shaft encoders. The linear position encoders define absolute linear positions based on movement between a stationary reference and the linearly displaced part. Rotary shaft encoders of the absolute type define an absolute angular position in a similar manner, except for the fact that they track changes in an angle.
Many of the prior art encoders, whether linear or rotary, can also determine a linear or an angular velocity. Additionally, they can determine total distance traveled in linear units (e.g., millimeters) or in angular units (in degrees or radians). Many other useful quantities can be derived from these measured parameters including, for example, angular acceleration.
The demands for accuracy, precision and speed placed on modern encoders have pushed their engineering designers to mainly adapt non-contact measurements enabled by purely electronic, magnetoresistive or optical technologies. For example, many of today's most accurate encoders use the Hall effect (eddy currents) or optical solutions based on shadowing, self-imaging and interference. The electronic approaches, which are also very high performance, typically include inductive and/or capacitive solutions.
For decades now, the fields of linear and rotational motion measurement have been moving away from contact measurements altogether. Even the least problematic contacts, such as brush-type contacts that establish electrical connections, are susceptible to wear and produce some mechanical resistance. Thus, by now, encoders using contacts are not common and can only be found in low-speed applications such as manual volume or tuning controls (e.g., in a radio receiver).
As a result of this trend, there is a dearth of encoders relying on mechanical contact for providing position tracking solutions in applications where lower accuracy measurements of absolute angular and linear position are sufficient. In many applications, however, such lower-performance encoders would be perfectly suitable. Unfortunately, such encoders are not presently available.